Wireless communication method using trigger information, and wireless communication terminal

ABSTRACT

Provided is a wireless communication terminal that wirelessly communicates with a base wireless communication terminal. The wireless communication terminal includes: a transceiver; and a processor. The processor is configured to receive trigger information and data from the base wireless communication terminal by using the transceiver, and transmits ACK information indicating whether the data is received to the base wireless communication terminal based on the trigger information. The trigger information is information for triggering transmission of the wireless communication terminal.

TECHNICAL FIELD

The present invention relates to a wireless communication method usingtrigger information and a wireless communication terminal.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelesscommunication technology that can provide a rapid wireless Internetservice to the mobile apparatuses has been significantly spotlighted.The wireless communication technology allows mobile apparatusesincluding a smart phone, a smart pad, a laptop computer, a portablemultimedia player, an embedded apparatus, and the like to wirelesslyaccess the Internet in home or a company or a specific service providingarea.

One of most famous wireless communication technology is wireless LANtechnology. Institute of Electrical and Electronics Engineers (IEEE)802.11 has commercialized or developed various technological standardssince an initial wireless LAN technology is supported using frequenciesof 2.4 GHz. First, the IEEE 802.11b supports a communication speed of amaximum of 11 Mbps while using frequencies of a 2.4 GHz band. IEEE802.11a which is commercialized after the IEEE 802.11b uses frequenciesof not the 2.4 GHz band but a 5 GHz band to reduce an influence byinterference as compared with the frequencies of the 2.4 GHz band whichare significantly congested and improves the communication speed up to amaximum of 54 Mbps by using an Orthogonal Frequency DivisionMultiplexing (OFDM) technology. However, the IEEE 802.11a has adisadvantage in that a communication distance is shorter than the IEEE802.11b. In addition, IEEE 802.11g uses the frequencies of the 2.4 GHzband similarly to the IEEE 802.11b to implement the communication speedof a maximum of 54 Mbps and satisfies backward compatibility tosignificantly come into the spotlight and further, is superior to theIEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless communicationtechnology standards after the 802.11ac and 802.11ad, discussion forproviding a high-efficiency and high-performance wireless communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless communication technology environment,communication having high frequency efficiency needs to be providedindoors/outdoors under the presence of high-density terminals and baseterminals and various technologies for implementing the communicationare required.

Especially, as the number of devices using a wireless communicationtechnology increases, it is necessary to efficiently use a predeterminedchannel. Therefore, required is a technology capable of efficientlyusing bandwidths by simultaneously transmitting data between a pluralityof terminals and base terminals.

DISCLOSURE Technical Problem

An object of the present invention is to provide an efficient wirelesscommunication method using trigger information and a wirelesscommunication terminal.

Especially, an object of the present invention is to provide a wirelesscommunication method that supports communication with a plurality ofwireless communication terminals using trigger information and awireless communication terminal.

Technical Solution

According to an embodiment of the present invention, a wirelesscommunication terminal that wirelessly communicates with a base wirelesscommunication terminal includes: a transceiver; and a processor, whereinthe processor is configured to receive trigger information and data fromthe base wireless communication terminal through the transceiver, andtransmit ACK information indicating whether the data is received to thebase wireless communication terminal based on the trigger information,wherein the trigger information is information for triggeringtransmission of the wireless communication terminal.

The processor may be configured to obtain the trigger information froman MAC header of a MAC Protocol Data Unit (MPDU) transmitted from thebase wireless communication terminal.

The processor may be configured to obtain information on a Resource Unit(RU) allocated to the wireless communication terminal from the triggerinformation, and transmit the ACK information based on the informationon the RU allocated to the wireless communication terminal.

The processor may be configured to obtain length information indicatinga length of a PLCP Protocol Data Unit (PPDU) including the ACKinformation from the trigger information, and transmit the ACKinformation based on the length information.

The processor may be configured to transmit the ACK information and datato the base wireless communication terminal based on the lengthinformation.

The processor may be configured to transmit data to the base wirelesscommunication terminal based on a remaining length excluding a lengthrequired for transmission of the ACK information from a length indicatedby the length information.

The processor may be configured to receive an Aggregate-MPDU (A-MPDU)including a plurality of MPDUs through the transceiver, wherein theA-MPDU may include a trigger MPDU including the trigger information anda data MPDU including the data, wherein the trigger MPDU may be a firstMPDU among a plurality of MPDUs included in the A-MPDU.

The A-MPDU may further include a trigger MPDU including the triggerinformation in addition to the trigger MPDU.

The trigger information may include information indicating one or moreRUs allocated to a random access, wherein the processor may beconfigured to obtain a counter value randomly within a predeterminedrange, and determine whether to perform a random access based on thecounter value and the number of the one or more RUs allocated to therandom access.

When a random access is determined, the processor may be configured torandomly access any one of the one or more RUs allocated to the randomaccess.

According to an embodiment of the present invention, a base wirelesscommunication terminal that wirelessly communicates with a plurality ofwireless communication terminals includes: a transceiver; and aprocessor, wherein the processor may transmit trigger information to theplurality of wireless communication terminals through the transceiver,and receive ACK information indicating whether the data is received fromthe plurality of wireless communication terminals.

The processor may be configured to insert the trigger information into aMAC header of a MAC Protocol Data Unit (MPDU).

The trigger information may include information on a resource unit (RU)allocated to each of the plurality of wireless communication terminals.

The trigger information may include length information indicating alength of a PLCP Protocol Data Unit (PPDU) including the ACKinformation.

The processor may be configured to transmit an Aggregate-MPDU (A-MPDU)including a plurality of MPDUs through the transceiver, wherein theA-MPDU may include a trigger MPDU including the trigger information anda data MPDU including the data, wherein the trigger MPDU may be a firstMPDU among the plurality of MPDUs included in the A-MPDU.

The A-MPDU may further include a trigger MPDU including the triggerinformation in addition to the trigger MPDU.

The processor may be configured to transmit the trigger MPDU and thedata MPDU using a different Modulation & Coding Scheme (MCS) by usingthe transceiver.

According to an embodiment of the present invention, a method ofoperating a wireless communication terminal that wirelessly communicateswith a base wireless communication terminal includes: receiving triggerinformation and data from the base wireless communication terminal; andtransmitting ACK information indicating whether the data is received tothe base wireless communication terminal based on the triggerinformation, wherein the trigger information may be information fortriggering transmission of the wireless communication terminal.

The receiving of the trigger information and the data may includeobtaining the trigger information from a MAC header of a MAC ProtocolData Unit (MPDU) transmitted from the base wireless communicationterminal.

The obtaining of the trigger information from the MAC header may includeobtaining information on a Resource Unit (RU) allocated to the wirelesscommunication terminal from the trigger information, wherein thetransmitting of the ACK information may include transmitting the ACKinformation based on the information on the RU allocated to the wirelesscommunication terminal.

Advantageous Effects

An embodiment of the present invention provides an efficient wirelesscommunication method and a wireless communication terminal using triggerinformation.

In particular, an embodiment of the present invention provides awireless communication method and a wireless communication terminal thatsupport communication with a plurality of wireless communicationterminals using trigger information.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless LAN system according to an embodiment of thepresent invention.

FIG. 2 shows a wireless LAN system according to another embodiment ofthe present invention.

FIG. 3 shows a block diagram illustrating a configuration of a stationaccording to an embodiment of the inventive concept.

FIG. 4 shows a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 shows a process that a station sets an access point and a linkaccording to an embodiment of the present invention.

FIG. 6 shows a structure of an A-MPDU according to an embodiment of thepresent invention.

FIG. 7 shows a problem that may occur when an access point according toan embodiment of the present invention transmits an A-MPDU including atrigger MPDU to a plurality of stations.

FIG. 8 shows a method of transmitting an A-MPDU to increase thereception success rate of control information by a wirelesscommunication terminal according to an embodiment of the presentinvention.

FIG. 9 shows a method of setting an MCS in the same manner as an A-MPDUincluding only a data MPDU when a wireless communication terminalaccording to an embodiment of the present invention transmits an A-MPDUincluding a control MPDU.

FIG. 10 shows that a wireless communication terminal according to anembodiment of the present invention adds padding to an MPDU included inan A-MPDU.

FIG. 11 shows that a wireless communication terminal according to anembodiment of the present invention transmits control informationthrough a MAC header.

FIG. 12 shows a configuration of an MCA header when a wirelesscommunication terminal according to an embodiment of the presentinvention transmits control information through a MAC header.

FIG. 13 shows another configuration of an MCA header when a wirelesscommunication terminal according to an embodiment of the presentinvention transmits control information through a MAC header.

FIG. 14 shows a specific format of a trigger frame according to anembodiment of the present invention.

FIG. 15 shows that the wireless communication terminal according to theembodiment of the present invention transmits trigger informationthrough the MAC header of the MPDU included in the DL MU PPDU and thetrigger MPDU.

FIG. 16 illustrates a method of implicitly transmitting triggerinformation according to an embodiment of the present invention.

FIG. 17 shows a method of setting an ACK policy when a wirelesscommunication terminal transmits data through a cascading sequenceaccording to an embodiment of the present invention.

FIG. 18 illustrates a method for a wireless communication terminal torecover a cascading sequence when ACK information is not received in thecascading sequence according to an embodiment of the present invention.

FIG. 19 shows that a wireless communication terminal according to anembodiment of the present invention requests transmission of ACKinformation for an MPDU previously transmitted through a MAC header of adata MPDU.

FIG. 20 shows a method of setting an ACK policy by a wirelesscommunication terminal according to an embodiment of the presentinvention.

FIG. 21 shows a method of a wireless communication terminal to set anetwork allocation vector (NAV) for communication with a plurality ofwireless communication terminals according to an embodiment of thepresent invention.

FIG. 22 shows that a wireless communication terminal according to anembodiment of the present invention performs random access based on atrigger frame.

FIG. 23 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Parts notrelating to description are omitted in the drawings in order to clearlydescribe the present invention and like reference numerals refer to likeelements throughout.

Furthermore, when it is described that one comprises (or includes orhas) some elements, it should be understood that it may comprise (orinclude or has) only those elements, or it may comprise (or include orhave) other elements as well as those elements if there is no specificlimitation.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2015-0117584, Nos. 10-2105-0120537, Nos.10-2105-0129366, and Nos. 10-2105-0190457 filed in the KoreanIntellectual Property Office and the embodiments and mentioned itemsdescribed in the respective applications are included in the DetailedDescription of the present application.

FIG. 1 is a diagram illustrating a wireless communication systemaccording to an embodiment of the present invention. For convenience ofdescription, an embodiment of the present invention is described throughthe wireless LAN system. The wireless LAN system includes one or morebasic service sets (BSS) and the BSS represents a set of apparatuseswhich are successfully synchronized with each other to communicate witheach other. In general, the BSS may be classified into an infrastructureBSS and an independent BSS (IBSS) and FIG. 1 illustrates theinfrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a concept including a wireless LAN communication devicesuch as non-AP STA, or an AP, or both terms. A station for wirelesscommunication includes a processor and a transceiver and according tothe embodiment, may further include a user interface unit and a displayunit. The processor may generate a frame to be transmitted through awireless network or process a frame received through the wirelessnetwork and besides, perform various processing for controlling thestation. In addition, the transceiver is functionally connected with theprocessor and transmits and receives frames through the wireless networkfor the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless communicationsystem according to another embodiment of the present invention. Forconvenience of description, another embodiment of the present inventionis described through the wireless LAN system. In the embodiment of FIG.2, duplicative description of parts, which are the same as or correspondto the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN physical layer frame, or the like and may be embeddedin the station 100 or provided as an exterior. According to theembodiment, the transceiver 120 may include at least one transmit andreceive module using different frequency bands. For example, thetransceiver 120 may include transmit and receive modules havingdifferent frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. Accordingto an embodiment, the station 100 may include a transmit and receivemodule using a frequency band of 6 GHz or more and a transmit andreceive module using a frequency band of 6 GHz or less. The respectivetransmit and receive modules may perform wireless communication with theAP or an external station according to a wireless LAN standard of afrequency band supported by the corresponding transmit and receivemodule. The transceiver 120 may operate only one transmit and receivemodule at a time or simultaneously operate multiple transmit and receivemodules together according to the performance and requirements of thestation 100. When the station 100 includes a plurality of transmit andreceive modules, each transmit and receive module may be implemented byindependent elements or a plurality of modules may be integrated intoone chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 may be a modulator and/or demodulator whichmodulates wireless signal transmitted to the transceiver 120 anddemodulates wireless signal received from the transceiver 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality of transmitand receive modules using different frequency bands. That is, the AP 200according to the embodiment of the present invention may include two ormore transmit and receive modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a transmit and receive module using a frequency band of 6 GHz ormore and a transmit and receive module using a frequency band of 6 GHzor less. The respective transmit and receive modules may performwireless communication with the station according to a wireless LANstandard of a frequency band supported by the corresponding transmit andreceive module. The transceiver 220 may operate only one transmit andreceive module at a time or simultaneously operate multiple transmit andreceive modules together according to the performance and requirementsof the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 may be a modulatorand/or demodulator which modulates wireless signal transmitted to thetransceiver 220 and demodulates wireless signal received from thetransceiver 220. The processor 210 controls various operations such asradio signal transmission/reception of the AP 200 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

When data is transmitted using Orthogonal Frequency Division Modulation(OFDMA) or Multi Input Multi Output (MIMO), any one wirelesscommunication terminal may transmit data to a plurality of wirelesscommunication terminals simultaneously. Also, any one wirelesscommunication terminal may simultaneously receive data from a pluralityof wireless communication terminals. At this time, any one of thewireless communication terminals may transmit the trigger informationtriggering the data transmission of the plurality of wirelesscommunication terminals. The trigger information may include informationon transmission resources allocated to a plurality of wirelesscommunication terminals. A method of transmitting and receiving controlinformation including trigger information will be described withreference to FIGS. 6 to 23.

For convenience of description, any one wireless communication terminalthat communicates simultaneously with a plurality of wirelesscommunication terminals is referred to as a first wireless communicationterminal and a plurality of wireless communication terminals thatsimultaneously communicate with the first wireless communicationterminal are referred to as a plurality of second wireless communicationterminals. In addition, the first wireless communication terminal may bereferred to as a base wireless communication terminal (device). Inaddition, the first wireless communication terminal may be a wirelesscommunication terminal that allocates a communication medium resourceand performs scheduling in communication with a plurality of wirelesscommunication terminals. Specifically, the first wireless communicationterminal may perform the role of a cell coordinator. At this time, thefirst wireless communication terminal may be the access point 200. Inaddition, the second wireless communication terminal may be the station100 associated with the access point 200. In a specific embodiment, thefirst wireless communication terminal may be a wireless communicationterminal that allocates a communication medium resource and performsscheduling in an independent network, such as an ad-hoc network, whichis not connected to an external distribution service. In addition, thefirst wireless communication terminal may be at least one of a basestation, an eNB, and a transmission point TP.

The first wireless communication terminal may transmit data to theplurality of second wireless communication terminals. At this time, thefirst wireless communication terminal may transmit one aggregate frame(Aggregate-MPDU, A-MPDU) including a plurality of MPDUs to the secondwireless communication terminal. With reference to FIGS. 6 to 16, amethod of transmitting trigger information through the A-MPDU will bedescribed. The MPDU may be referred to herein as a MAC frame or a frame.

FIG. 6 shows a structure of an A-MPDU according to an embodiment of thepresent invention.

MPDU is the data processing unit of the Mac layer. Specifically, theMPDU includes an MAC header and an FCS for verifying whether there is anerror in an MSDU or an aggregate MSDU (A-MSDU), which is a dataprocessing unit of an upper layer. The A-MPDU includes a plurality ofMPDUs, and includes a delimiter for distinguishing a plurality of MPDUsand a pad for adjusting a transmission length.

The delimiter includes an End-of-Frame (EOF) field indicating whetherthe MPDU is the last MPDU, an MPDU Length field indicating a length ofthe MPDU, a CRC field, and a signature field.

Also, when the A-MPDU includes a maximum of N MPDUs, the value indicatedby the bitmap of the Block Ack (BA) indicating whether or not each ofthe plurality of MPDUs included in the A-MPDU is received may be N. In aspecific embodiment, N may be 64 or 256.

The PLCP Protocol Data Unit (PPDU) for transmitting the A-MPDU includesa PHY header indicating information related to the physical layer. ThePHY header includes an L-SIG field including information decodable bythe legacy wireless communication terminal.

The L-SIG field includes an L-Rate field and an L-Length field. TheL-Rate field and the L-Length field indicate information on the durationof the PPDU including the L-SIG field. Specifically, when the L-Rate is6 Mbps, which is the minimum rate of the OFDM frame, the maximum numberof symbols that L-Length may represent is 1365 or 1366 symbols. SinceOFDM takes 4 us per symbol, the L-Rate/L-Length field may represent aduration of 5.460 ms or 5.464 ms at most. Since the legacy wirelesscommunication terminal may decode the L-SIG, the legacy wirelesscommunication terminal may calculate the duration of the PPDU after theL-SIG based on the L-Rate field and the L-Length field. Accordingly, thelegacy wireless communication terminal does not access the correspondingchannel during the PPDU duration after the L-SIG. Therefore, thewireless communication terminal may prevent the collision with thetransmission of the legacy wireless communication terminal through theL-SIG field when transmitting the A-MPDU.

The A-MPDU may include not only a data MPDU including data but also acontrol MPDU including control information or a management MPDUincluding management information. In a specific embodiment, the A-MPDUmay include at least one of the control MPDU and the management MPDUwith the data MPDU. Specifically, the A-MPDU is a kind of data MPDU andcontrol MPDU, and may include a trigger MPDU including triggerinformation. This will be described with reference to FIG. 7.

FIG. 7 shows a problem that may occur when an access point according toan embodiment of the present invention transmits an A-MPDU including atrigger MPDU to a plurality of stations.

The first wireless communication terminal may transmit the triggerinformation for triggering the data transmission of each of theplurality of second wireless communication terminals while transmittingdata to the plurality of second wireless communication terminals.Specifically, the first wireless communication terminal may transmit thedata MPDU and the trigger MPDU together through the A-MPDU.

Also, each of the first wireless communication terminal and the secondwireless communication terminal may transmit an ACK MPDU indicatingwhether data is received through the A-MPDU together with the data MPDU.

In this way, when the wireless communication terminal transmits the dataMPDU and the control MPDU through the A-MPDU and the transmission of thecontrol MPDU fails, the efficiency of the wireless communication maydeteriorate.

For example, as in the embodiment of FIG. 7(a), the access pointtransmits the A-MPDU including the trigger frame (MPDU) together withthe data MPDU while transmitting a Down Link (DL) Multi-User (MU) PPDUto the first station STA1 and the second station STA2. At this time, ifthe first station STA1 fails to receive the trigger MPDU, the wirelesscommunication resources allocated to the first station STA1 are wasted.Also, the first station STA1 loses transmission opportunity. Therefore,in such a case, the access point must grant the transmission opportunityto the first station STA1 again.

Further, when the first station STA1 transmits data and a BA MPDUtogether as in the embodiment of FIG. 7 (b), the access point may notreceive the BA MPDU. Therefore, it is necessary for the access point tosolicit BA frame transmission by transmitting a BA Request (BAR) frame.

Also, as in the embodiment of FIG. 7C, after receiving the Up Link (UL)MU PPDU from the first station STA1 and the second station STA2, theaccess point transmits the A-MPDU including the BA MPDU for the receivedUL MU PPDU to the first station STA1 and the second station STA2 whentransmitting the DL MU PPDU. At this time, the first station STA1 maynot receive the BA MPDU transmitted from the access point. Therefore,the first station STA1 needs to transmit the BAR MPDU to the accesspoint to solicit the transmission of the BA frame.

In such a way, if the transmission of the control frame transmittedthrough the A-MPDU fails, an additional recovery procedure is required.When the wireless communication terminal performs the additionalrecovery procedure, the transmission efficiency of the wirelesscommunication terminal is lowered. A wireless communication method forincreasing the transmission success rate of a control frame will bedescribed with reference to FIGS. 8 to 16.

FIG. 8 shows a method of transmitting an A-MPDU for increasing thesuccess rate of receipt of control information by a wirelesscommunication terminal according to an embodiment of the presentinvention.

As described above, the wireless communication terminal may transmit theA-MPDU including the data MPDU and the control MPDU (or the managementMPDU). Specifically, when transmitting a DL MU PPDU or an UL MU PPDU asshown in FIG. 8(a), the wireless communication terminal may transmit anA-MPDU including a data MPDU and a control MPDU. At this time, thecontrol MPDU may be the trigger MPDU described above. At this time, thewireless communication terminal may increase the transmission successrate of the control frame through the embodiment of the presentinvention.

The wireless communication terminal may determine the transmission orderof the control MPDU among the plurality of MPDUs included in the A-MPDUdifferently from the transmission order of the data MPDU. Specifically,the wireless communication terminal may transmit the control MPDU lastamong the plurality of MPDUs included in the A-MPDU as in the embodimentof FIG. 8(b).

In another specific embodiment, the wireless communication terminal maytransmit the control MPDU first among the plurality of MPDUs included inthe A-MPDU as in the embodiment of FIG. 8(c). At this time, the controlMPDU may be a trigger MPDU or a BA MPDU as described above. In addition,when the A-MPDU includes both the trigger MPDU and the BA MPDU, thewireless communication terminal may transmit the BA MPDU as the firstMPDU. The wireless communication terminal receives training fields suchas HE-STF and HE-LTF, estimates the channel based on the training field,and performs Automatic Gain Control (AGC). Therefore, as the time passesafter receiving the training signal, the reception accuracy of thewireless communication terminal becomes poor. Therefore, whentransmitting the first of the plurality of MPDUs included in the A-MPDU,the wireless communication terminal may increase the transmissionsuccess rate of the control MPDU.

In another specific embodiment, the wireless communication terminal maydetermine the order of transmitting the control MPDU according to thetransmission success rate for each transmission order of the pluralityof MPDUs included in the A-MPDU as in the embodiment of FIG. 8(d). Thewireless communication terminal may determine which MPDU of theplurality of MPDUs included in the A-MPDU fails to be transmittedthrough the BA frame. Therefore, the wireless communication terminal maydetermine the transmission success rate for each transmission order ofthe plurality of MPDUs included in the A-MPDU. After determining thetransmission success rate for each transmission order of the pluralityof MPDUs, the wireless communication terminal may transmit the controlMPDUs in a transmission order with a high transmission success rate.

The wireless communication terminal may repeatedly transmit the controlMPDU in the A-MPDU as in the embodiment of FIG. 8(e). When the wirelesscommunication terminal repeatedly transmits the same control MPDU, thetransmission success rate of the corresponding control MPDU increases.In addition, the control MPDU including the control information does nothave a larger MPDU size than the data MPDU. Therefore, the control MPDUis repeatedly transmitted, so that the occurring overhead is small.

The wireless communication terminal may perform the method of modulatingthe control MPDU included in the A-MPDU differently from the method ofmodulating the data MPDU included in the A-MPDU. In a specificembodiment, when transmitting the control MPDU as in the embodiment ofFIG. 8(f), the wireless communication terminal may use a more robust MCSthan the MCS used to transmit the data MPDU. To explain the concretewireless communication operation, FIGS. 9 and 10 will be describedfirst.

FIG. 9 shows a method of setting an MCS in the same manner as an A-MPDUincluding only a data MPDU when a wireless communication terminalaccording to an embodiment of the present invention transmits an A-MPDUincluding a control MPDU.

As in the embodiment of FIG. 9(a), when a station transmits data to anaccess point, the station may use a high rate MCS to increase the datatransmission rate. When transmitting a control frame, i.e., a triggerMPDU, and a multi-station BA (M-STA BA) MPDU, the access point may use amore robust MCS than the MCS used for data transmission in order toincrease the transmission success rate.

However, as in the embodiment of FIG. 9(b), when an access point and astation transmit an A-MPDU including a data MPDU and a control MPDUtogether, the access point and the station use a high-rate MCS tooptimize the transmission of data MPDUs. Therefore, the probability ofoccurrence of transmission failure of the control MPDU increases.Therefore, when transmitting the control MPDU, the wirelesscommunication terminal may use a more robust MCS than the MCS used totransmit the data MPDU.

In a specific embodiment, the wireless communication terminal maytransmit the control MPDU in a fixed order to the predetermined MCS.Accordingly, the wireless communication terminal may not transmitadditional information signaling the MCS of the control MPDU. In anotherspecific embodiment, the wireless communication terminal may signal atleast one of the MCS used for transmitting the control MPDU and theposition of the control MPDU in the A-MPDU through the delimiterincluded in the A-MPDU. In another specific embodiment, the wirelesscommunication terminal may transmit an OFDM symbol of a predeterminedlocation of the PPDU to a fixed MCS. At this time, the fixed MCS may bea relatively robust MCS, and the wireless communication terminal maytransmit the control MPDU through an OFDM symbol of a predeterminedlocation.

However, when the wireless communication terminal uses a more robust MCSthan the MCS used to transmit the data MPDU when transmitting thecontrol MPDU, the wireless communication terminal may change the MCS byeach OFDM symbol unit. In such a case, the wireless communicationterminal needs to add padding to the MPDU. This will be described withreference to FIG. 10.

FIG. 10 shows that a wireless communication terminal according to anembodiment of the present invention adds padding to an MPDU included inan A-MPDU.

The wireless communication terminal may transmit the A-MPDU includingthe control MPDU and the data MPDU together as shown in FIG. 10(a). Atthis time, the wireless communication terminal may transmit the controlMPDU and the data MPDU to different MCSs as shown in FIG. 10(b).

The wireless communication terminal constructs a PPDU for each OFDMsymbol and communicates, so that the MCS may be changed for each OFDMsymbol. Therefore, in order to transmit the control MPDU and the dataMPDU to different MCSs, the wireless communication terminal may add anadditional padding in addition to the padding (called Padding-A) between0 and 3 bytes added for each MPDU in order for transmission in units of4 bytes. At this time, the additional padding is called Padding-B.

The wireless communication terminal may obtain the length of thePadding-A through the length of the MPDU signaled by the MPDU delimiter.In the case of Padding-B, which is added for the MCS change per MPDU,the time point that the combination of the data of the correspondingMPDU subframe and the Padding-A ends may not fill the OFDM symbol asshown in FIG. 10(c). The wireless communication terminal may grasp theamount of data remaining to the nearest OFDM symbol boundary, and thusmay know the length of Padding-B. Therefore, there is no need forseparate signaling for the length of Padding-B.

Referring back to FIG. 8, the operation of the wireless communicationterminal according to the embodiment of the present invention will bedescribed.

In another specific embodiment, when transmitting the control MPDU as inthe embodiment of FIG. 8(g), the wireless communication terminal may usea more robust FEC code than the FEC code used when transmitting the dataMPDU. In addition, the wireless communication terminal may apply the FECcode to the transmission of at least one of the delimiters fordistinguishing the MAC header from the control MPDU for protection ofthe control MPDU.

In relation to the embodiments described with reference to FIGS. 8 to10, the wireless communication terminal changes the transmission methodof the control MPDU included in the A-MPDU. The wireless communicationterminal may increase the control information transmission probabilityby transmitting the control information through the MAC header insteadof the control MPDU. This will be described with reference to FIGS. 11to 14.

FIG. 11 shows that a wireless communication terminal according to anembodiment of the present invention transmits control informationthrough a MAC header.

The wireless communication terminal may transmit control informationthrough the MAC header included in the DL MPDU or the UL MPDU.Specifically, the wireless communication terminal may transmit controlinformation through the MAC header of one or more MPDUs included in theDL/UL A-MPDU. At this time, the control information may be transmittedby the number of MPDUs included in the A-MPDU. When control informationis transmitted through the MAC header of a plurality of MPDUs, when anyone MPDU among a plurality of MPDUs included in the A-MPDU issuccessfully transmitted, the control information included in the MACheader of the corresponding MPDU is also successfully transmitted.Therefore, when the control information is transmitted through the MACheader of a plurality of MPDUs included in the A-MPDU, the probabilityof transmission failure of the control information may be less than thecase that the control information is transmitted through the separatecontrol MPDU.

In addition, the MAC header including the control information may beincluded in the data MPDU including the data. Through this, the wirelesscommunication terminal may transmit data and control informationtogether.

At this time, the control information may be at least one of theabove-described trigger information and Block ACK information indicatingwhether individual MPDUs are received or not. In a specific embodiment,the trigger information included in the MAC header may be part of thetrigger information included in the trigger frame. For example, thetrigger information included in the MAC header may include informationon a Resource Unit (RU) assigned to the wireless communication terminaland information indicating the length of the PPDU that the wirelesscommunication terminal may transmit. The RU indicates a unit frequencyband allocated to the second wireless communication terminal by thefirst wireless communication terminal. In addition, for example, theBlock ACK information included in the MAC header may be a part or all ofthe Block ACK information included in the BA frame.

In the embodiment of FIG. 11(a), the access point AP transmits theA-MPDU including the data MPDU and the trigger MPDU to the first stationSTA1 to the third station STA3. In addition, the access point AP maytransmit the trigger information through the MAC headers of theplurality of MPDUs included in the A-MPDU.

At this time, it is assumed that the transmission of the trigger MPDUthat the access point AP transmits to the first station STA1 fails.

However, the first station STA1 obtains the trigger information from theMAC header of the data MPDU included in the A-MPDU transmitted from theaccess point AP. The first station STA1 transmits the A-MPDU includingthe BA MPDU and the data MPDU to the access point AP based on theacquired trigger information.

In the embodiment of FIG. 11(b), the access point AP transmits theA-MPDU including the data MPDU and the trigger MPDU to the first stationSTA1 to the third station STA3.

The first to third stations STA1 to STA3 receive the A-MPDU from theaccess point AP and acquire the data MPDU and the trigger MPDU. Inaddition, the first to third stations STA1 to STA3 acquire triggerinformation from the trigger MPDU.

The first to third stations STA1 to STA3 transmit the A-MPDU includingthe BA MPDU and the data MPDU to the access point AP based on theacquired trigger information. Also, the first to third stations STA1 toSTA3 may transmit Block ACK information through the MAC header of aplurality of MPDUs included in the A-MPDU.

At this time, it is assumed that the transmission of the BA MPDU thatthe first station STA1 transmits to the access point AP fails.

However, the access point AP acquires Block ACK information of the firststation STA1 through the MAC header of the data MPDU included in theA-MPDU transmitted from the first station STA1.

In the embodiment of FIG. 11, although the control information istransmitted through the MAC header of the data MPDU and a separatecontrol MPDU, the control information may be transmitted only throughthe MAC header of the data MPDU without transmitting the separatecontrol MPDU.

In another specific embodiment, the wireless communication terminal mayset the ACK Policy of the data to Delayed Block ACK in preparation fortransmission failure of control information when transmitting data andcontrol information at the same time. In this case, the wirelesscommunication terminal may separately request BA from the wirelesscommunication terminal that receives the data MPDU after transmittingthe data MPDU. Specifically, the wireless communication terminal maytransmit a data MPDU to a plurality of wireless communication terminals,and may transmit a BA Request (BAR) frame for requesting BA from aplurality of wireless communication terminals that receive the dataMPDU. In particular, when the wireless communication terminal fails toreceive the BA for the data MPDU from the wireless communicationterminal that receives the data MPDU, the wireless communicationterminal may transmit a BA Request (BAR) frame for requesting the BAfrom the wireless communication terminal that receives the data MPDU.

The specific format of the trigger information included in the MACheader described with reference to FIG. 11 will be described withreference to FIGS. 12 to 14.

FIG. 12 shows a configuration of an MCA header when a wirelesscommunication terminal according to an embodiment of the presentinvention transmits control information through a MAC header.

As described above, the wireless communication terminal may transmit thetrigger information through the MAC header of the MPDU included in theDL PPDU when transmitting the DL PPDU. In particular, when the firstwireless communication terminal transmits a DL MU PPDU to a plurality ofsecond wireless communication terminals, as in the embodiment of FIG.12(a), trigger information may be transmitted through the MAC header ofthe MPDU in the A-MPDU included in the DL MU PPDU. At this time, theplurality of second wireless communication terminals may transmit ACKinformation indicating whether or not the DL MU PPDU is received to thefirst wireless communication terminal based on the trigger information.Specifically, the plurality of second wireless communication terminalsmay transmit the UL MU PPDU including the ACK information indicatingwhether the DL MU PPDU is received to the first wireless communicationterminal based on the trigger information.

At this time, the trigger information may include RU allocationinformation indicating an RU allocated to the second wirelesscommunication terminal for UL PPDU transmission. In addition, thetrigger information may include UL PPDU length information indicatingthe length of UL PPDUs that is transmitted from the second wirelesscommunication terminal.

The RU allocation information may indicate an RU allocated to the secondwireless communication terminal as an index. Specifically, the firstwireless communication terminal may occupy a frequency band having abandwidth of 20 MHz, 40 MHz, 80 MHz, and a maximum of 160 MHz. Thesecond wireless communication terminal must transmit the UL PPDU usingthe RU designated by the first wireless communication terminal in themaximum band occupied by the first wireless communication terminal. Atthis time, the first wireless communication terminal should be able todivide the 20 MHz bandwidth into 9 RUs and represent 72 or moreindividual RUs in a maximum 160 MHz bandwidth, as in the embodiment ofFIG. 12(b). For this, the RU allocation information may be a 7-bit fieldindicating the index of the RU.

In another embodiment, the first wireless communication terminal mayvariably change the bit field indicating the index of the RU under theassumption that the second wireless communication terminal may transmitACK information on the DL PPDU only within the bandwidth occupied by theDL PPDU. For example, when the first wireless communication terminaltransmits the DL PPDU in units of 40 MHz, the second wirelesscommunication terminal may transmit the ACK information on the DL PPDUonly within the frequency band in which the DL PPDU is received. In thiscase, the first wireless communication terminal may indicate an RUassigned to the second wireless communication terminal among 18 RUs asan index. For this, the RU allocation information may be a 5-bit fieldindicating the index of the RU in the band occupied by the DL PPDU.

The first wireless communication terminal may transmit the UL PPDUlength information through the Duration/ID field of the MAC header.Specifically, the first wireless communication terminal may set thevalue of the Duration/ID field of the MAC header of the DL PPDUtransmitted from the first wireless communication terminal to a valueobtained by adding the length of the corresponding DL PPDU as well asthe length of the UL PPDU to be transmitted from the second wirelesscommunication terminal. In another specific embodiment, the firstwireless communication terminal may set the value of the Duration/IDfield to a value obtained by adding the length of the DL PPDU, the timeinterval until the transmission of the UL PPDU starts after thereception of the DL PPDU, and the length of the UL PPDU.

Also, the first wireless communication terminal may transmit the triggerinformation through the MAC header of all the MPDUs included in the DLPPDU. Through this, the transmission probability of the triggerinformation may be increased.

The second wireless communication terminal acquires the triggerinformation based on the MAC header of the MPDU included in the DL PPDU.Specifically, the second wireless communication terminal may acquire thetrigger information from the MAC header of the MPDU included in the DLPPDU. In a specific embodiment, the second wireless communicationterminal may obtain RU allocation information from the MAC header of theMPDU included in the DL PPDU. The second wireless communication terminalmay transmit ACK information indicating whether the MPDU included in theDL PPDU is received to the first wireless communication terminal basedon the RU allocation information. At this time, the ACK information maybe Block ACK information.

The second wireless communication terminal may obtain the UL PPDU lengthinformation from the MAC header of the MPDU included in the DL PPDU.Also, the second wireless communication terminal may transmit ACKinformation and data together as described above. At this time, thesecond wireless communication terminal may transmit ACK informationindicating whether the data and the MPDU included in the DL PPDU arereceived based on the UL PPDU length information. Specifically, thesecond wireless communication terminal may transmit data based on theremaining length excluding the length required for transmitting the ACKinformation indicating whether the MPDU included in the DL PPDU isreceived from the length indicated by the UL PPDU length information.For example, the second wireless communication terminal may transmitdata having a length less than the remaining length excluding the lengthrequired for transmitting ACK information indicating whether the MPDUincluded in the DL PPDU is received from the length indicated by the ULPPDU length information.

FIG. 13 shows another configuration of an MCA header when a wirelesscommunication terminal according to an embodiment of the presentinvention transmits control information through a MAC header.

As described above, the first wireless communication terminal maytransmit the trigger information to the plurality of second wirelesscommunication terminals through the MAC header of the MPDU included inthe DL MU PPDU. At this time, the plurality of second wirelesscommunication terminals may transmit the UL MU PPDU including the ACKinformation indicating whether the DL MU PPDU is received based on thetrigger information. In a specific embodiment, in relation to the firstwireless communication terminal, the DL MU PPDU may transmit triggerinformation through a trigger MPDU separate from the MAC header of theMPDU, as in the embodiment of FIG. 13(a).

The concrete format of the MAC header of the MPDU included in the DL MUPPDU may be the same as the embodiment of FIG. 13(b). The MAC header ofthe MPDU includes an HE Control field. The HE Control field is a fieldwhose concrete format varies depending on the type of Controlinformation included in the MAC header. At this time, the HE Controlfield of the MAC header may include trigger information.

The specific format of the trigger information may be the same as theembodiment of FIG. 13(c). The trigger information may include the RUallocation information and UL PPDU length information described above.In relation to the second wireless communication terminal, theinformation not included in the trigger information included in the MACheader may transmit the UL PPDU by referring to the trigger informationof the trigger frame. In a specific embodiment, the size of the fieldindicating the UL PPDU length information included in the triggerinformation included in the MAC header may be smaller than the size ofthe field indicating the UL PPDU length information in the triggerframe. Specifically, the field indicating the UL PPDU length informationincluded in the trigger information included in the MAC header is a9-bit field, and the field indicating the UL PPDU length information inthe trigger frame may be a 12-bit field. This is because the length ofthe UL PPDU according to the trigger information included in the MACheader may be shorter than the length of the UL PPDU according to thetrigger frame.

At this time, the second wireless communication terminal may set thevalue of the L_LENGTH field of the L-SIG included in the UL PPDU byreferring to the value of the UL PPDU length information.

The RU allocation information includes information on a channel, whichis a frequency band having a bandwidth of 20 MHz allocated by the secondwireless communication terminal, information on the type of RU includedin the channel, and information indicating how many frequency bands areallocated to the second wireless communication terminal. At this time,if the second wireless communication terminal is designated to transmitthe UL PPDU only through the channel on which the data is received, theinformation on the channel may be omitted.

The specific format of the RU allocation information included in thetrigger information included in the MAC header may be the same as theformat of the RU allocation information included in the trigger frame.The format of the RU allocation information included in the triggerframe will be described in detail with reference to the structure of thetrigger frame in FIG. 14.

FIG. 14 shows a concrete format of a trigger MPDU according to anembodiment of the present invention.

The first wireless communication terminal may trigger the datatransmission of the plurality of second wireless communication terminalsby transmitting the trigger frame to the plurality of second wirelesscommunication terminals. At this time, the first wireless communicationterminal may transmit the same trigger frame for each 20 MHz frequencyband.

In the embodiment of FIG. 14(a), the access point transmits a triggerframe to the first station STA1 to the tenth station STA10. At thistime, the access point transmits the same trigger frame every 20 MHzbandwidth. In another specific embodiment, the access point may transmitthe trigger frame through the entire 40 MHz frequency band.

The first to tenth stations STA1 to STA10 transmit data to the accesspoint based on the trigger frame.

The trigger frame includes a Frame Control field, a Duration/ID field,an Address1 field, an Address2 field, a Frame Body field, and an FCSfield.

At this time, the Frame Body field includes a Common Info fieldindicating information commonly applied to the second wirelesscommunication terminal receiving the trigger frame, and a Per User Infofield indicating information applied to the second wirelesscommunication terminal.

The Common Info field includes a UL PPDU Length field, a SIG-A Infofield, a CP+HE LTF Type field, and a Trigger Type field.

The UL PPDU Length field indicates the length of the UL PPDU transmittedfrom the second wireless communication terminal. The second wirelesscommunication terminal may set the value of the L_LENGTH field of theL-SIG included in the UL PPDU to the value of the UL PPDU lengthinformation.

The SIG-A Info field indicates information to be included in the SIG-Awhen the second wireless communication terminal transmits the UL PPDU.Specifically, the SIG-A Info field may indicate at least one of afrequency bandwidth, a BSS color, and a TXOP duration of an UL PPDU tobe included in the SIG-A when the second wireless communication terminaltransmits the UL PPDU. At this time, the TXOP indicates a time durationduring which the wireless communication terminal may performtransmission without additional contention procedure.

The CP+HE LTF Type field indicates a Cyclic Prefix (CP) length and atype of LTF to be applied when the second wireless communicationterminal transmits the UL PPDU.

The Trigger Type field indicates the transmission type of the UL PPDUtriggered by the trigger frame. Specifically, the transmission type ofUL PPDU indicated by the Trigger Type field may indicate at least one ofdata transmission, simultaneous CTS transmission, and buffer statusreport (BSR) transmission.

The Per User Info field includes an AID field, an MCS field, a Codingfield, an RU allocation field, an SS allocation field, and a DCM field.

The AID field indicates a second wireless communication terminalcorresponding to Per User Info.

The MCS field indicates an MCS to be used by the second wirelesscommunication terminal when transmitting the UL PPDU.

The Coding field indicates a coding type to be used when the secondwireless communication terminal transmits the UL PPDU. The coding typemay indicate at least one of BCC and LDPC.

The RU allocation field is RU allocation information indicating an RUallocated to the second wireless communication terminal by the firstwireless communication terminal. Specifically, the RU allocation fieldincludes information CH on a channel, which is a frequency band having abandwidth of 20 MHz, information RA on the type of RU included in thechannel, and information STA index indicating how many frequency bandsare allocated to the second wireless communication terminal.

For example, it is assumed that the value of the RU allocation fieldcorresponding to the tenth station STA10 in the embodiment of FIG. 14(a)is 2nd 20 MHz, 00001111, and 5. At this time, the channel allocated tothe tenth station STA10 is the second 20 MHz band. Also, the channelallocated to the tenth station STA10 is divided into RUs composed of52/52/26/52/52 subcarriers. Also, the tenth station STA10 indicates thatthe last 52 RUs, which is the fifth of the corresponding channel, isallocated.

The SS allocation field indicates the number of spatial streams to betransmitted in the allocated RU when the second wireless communicationterminal transmits the UL PPDU.

The DCM field indicates whether or not the second wireless communicationterminal applies Dual Carrier Modulation (DCM) when transmitting the ULPPDU.

When the first wireless communication terminal transmits the triggerinformation through the MAC header of the MPDU included in the DL MUPPDU, the transmission probability of the trigger information may beincreased. At this time, the first wireless communication terminal maytransmit the trigger information through the trigger MPDU in addition tothe MAC header of the MPDU included in the DL MU PPDU. Through this, thefirst wireless communication terminal may further increase thetransmission probability of the trigger information. This will bedescribed with reference to FIG. 15.

FIG. 15 shows that the wireless communication terminal according to theembodiment of the present invention transmits trigger informationthrough the MAC header of the MPDU included in the DL MU PPDU and thetrigger MPDU.

In the embodiment of FIG. 15(a), the access point AP transmits theA-MPDU including the data and the unicast trigger MPDU to the firststation STA1 to the third station STA3. In addition, the access pointtransmits a broadcast trigger MPDU to the fifth and sixth stations STA5and STA6. At this time, the first to fourth stations STA1 to STA4transmit data and a BA MPDU to the access point based on the unicasttrigger MPDU. In addition, the fifth to sixth stations STA5 to STA6transmit data to the access point based on the broadcast trigger MPDU.

At this time, if at least one of the first to fourth stations STA1 toSTA4 fails to receive the unicast trigger MPDU, some frequency bands arewasted. However, it is possible to prevent the access point fromtransmitting the trigger information through the MAC header of the MPDUincluded in the DL MU PPDU.

For example, in the embodiment of FIG. 15(b), the access point alsotransmits trigger information through the MAC header of the MPDUincluded in the DL MU PPDU. At this time, even if the first to fourthstations STA1 to STA4 fail to receive the unicast trigger MPDU, thefirst to fourth stations STA1 to STA4 may transmit data and a BA MPDU tothe access point based on the MAC header of the MPDU included in the DLMU PPDU.

In addition, as in the embodiment of FIG. 15(c), even if the first tofourth stations STA1 to STA4 fail to receive the data MPDU, the first tofourth stations STA1 to STA4 may transmit data to the access point basedon the unicast trigger MPDU.

At this time, the trigger information included in the trigger MPDU andthe trigger information included in the MAC header of the MPDU includedin the DL MU PPDU may be the same. If the contents of the triggerinformation included in the trigger MPDU and the trigger informationincluded in the MAC header of the MPDU included in the DL MU PPDU arenot the same, the second wireless communication terminal may givepriority to the late received information. In addition, the secondwireless communication terminal may operate according to the informationincluded in the trigger MPDU with respect to the trigger information notincluded in the MAC header of the MPDU included in the DL MU PPDU.

When the second wireless communication terminal transmits the ACKinformation to the first wireless communication terminal according to apredetermined rule, the first wireless communication terminal may notexplicitly transmit the trigger information. This reduces the overheadrequired to transmit trigger information. This will be described withreference to FIG. 16.

FIG. 16 illustrates a method of implicitly transmitting triggerinformation according to an embodiment of the present invention.

The second wireless communication terminal may transmit ACK informationon the MPDU included in the DL PPDU to the first wireless communicationterminal through the frequency band on which the DL PPDU is received.For example, in the embodiment of FIG. 16(a), each of the first stationSTA1 to the third station STA3 transmits a BA MPDU for received data tothe access point through a frequency band on which data is received fromthe access point. Through this, the second wireless communicationterminal may transmit ACK information on the MPDU included in the DLPPDU transmitted from the first wireless communication terminal to thefirst wireless communication terminal without receiving the separatetrigger information. If a wide frequency band is allocated to the secondwireless communication terminal during DL PPDU transmission, the secondwireless communication terminal transmits ACK information through a widefrequency band. Therefore, a frequency band may be wasted.

The second wireless communication terminal may transmit ACK informationon the MPDU included in the DL PPDU to the first wireless communicationterminal through a part of the frequency band on which the DL PPDU isreceived. Specifically, the second wireless communication terminal maytransmit ACK information on the MPDU included in the UL PPDU using afrequency band of a predetermined bandwidth among the frequency bands inwhich the DL PPDU is received. For example, in the embodiments of FIGS.16(b) and 16(c), the third station STA3 transmits BA MPDUs for datausing only a part of the frequency bands in which data is received. Atthis time, some of the frequency bands used by the second wirelesscommunication terminal may be the lowest frequency band among thefrequency bands in which the DL PPDU is received. In another specificembodiment, some of the frequency bands used by the second wirelesscommunication terminal may be the highest frequency band among thefrequency bands in which the DL PPDU is received. In another specificembodiment, some of the frequency bands used by the second wirelesscommunication terminal may be a predetermined position in the frequencyband in which the DL PPDU is received.

The second wireless communication terminal other than the secondwireless communication terminal that transmits ACK information maytransmit data through a frequency band other than the frequency bandused for ACK information transmission. At this time, the second wirelesscommunication terminal other than the second wireless communicationterminal that transmits the ACK information may transmit data throughthe discontinuous frequency band like the fourth station STA4 in theembodiment of FIG. 16(b). In another specific embodiment, the secondwireless communication terminal other than the second wirelesscommunication terminal transmitting the ACK information may transmitdata through a continuous frequency band like the fourth station STA4 inthe embodiment of FIG. 16(c). At this time, in order for the secondwireless communication terminal other than the second wirelesscommunication terminal transmitting the ACK information to transmit datathrough the continuous frequency band, the first wireless communicationterminal may allocate a certain frequency band to the second wirelesscommunication terminal that transmits the ACK information. Through suchan operation, it is possible to reduce waste of the frequency band whentransmitting the ACK information of the second wireless communicationterminal.

Also, through some of the frequency bands in which the DL PPDU isreceived, the second wireless communication terminal may repeatedlytransmit the ACK information on the MPDU included in the DL PPDU in thefrequency domain to the first wireless communication terminal.Specifically, through the unassigned frequency band for datatransmission among the frequency bands in which the DL PPDU is received,the second wireless communication terminal may repeatedly transmit theACK information on the MPDU included in the DL PPDU in the frequencydomain to the first wireless communication terminal. For example, in theembodiment of FIG. 16(d), the first station STA1 repeatedly transmits BAin a frequency band not allocated to another station among the frequencybands in which data is received. Through such an operation, the secondwireless communication terminal may increase the transmissionprobability of the ACK information.

Referring to FIGS. 6 to 16, an embodiment of a method of transmittingcontrol information has been described. A transmission failure may occureven if the transmission probability of the control information isincreased. Therefore, if transmission of control information fails, amethod for recovering it is needed. This will be described withreference to FIGS. 17 to 19.

FIG. 17 shows a method of setting an ACK policy when a wirelesscommunication terminal transmits data through a cascading sequenceaccording to an embodiment of the present invention.

The first wireless communication terminal and the second wirelesscommunication terminal may transmit data and receive data in one TXOP.That is, DL MU PPDU transmission and UL MU PPDU transmission may beperformed in one TXOP. At this time, the first wireless communicationterminal may transmit the trigger information to the second wirelesscommunication terminal. The second wireless communication terminal maytransmit data to the first wireless communication terminal based on thetrigger information. The case that the first wireless communicationterminal and the second wireless communication terminal transmit dataand receive data in one TXOP is referred to as a cascading sequence.

In addition, the wireless communication terminal may designate a methodof a wireless communication terminal receiving data to transmit ACKindicating whether or not the data is received, at the time of datatransmission. An ACK transmission method indicating whether data isreceived is referred to as an ACK policy. The wireless communicationterminal receiving the data transmits the ACK information to thewireless communication terminal transmitting the data according to theACK policy. In a specific embodiment, when the QoS Data MPDU istransmitted, the ACK policy may be included in the subfield in the QoSControl field in the MAC Header.

The ACK policy may be classified as in the embodiment of FIG. 17(d).Specifically, the ACK policy may indicate that the wirelesscommunication terminal receiving the data transmits ACK informationimmediately after data reception. At this time, “immediately” mayindicate that ACK information is transmitted without transmitting otherinformation. In addition, when the wireless communication terminal thattransmits the data fails to receive the ACK information from thewireless communication terminal that receives the data, the wirelesscommunication terminal may transmit a Block Ack Request (BAR) MPDU tothe wireless communication terminal that receives the data. In anotherexemplary embodiment, when the wireless communication terminal thattransmits the data fails to receive the ACK information from thewireless communication terminal that receives the data, the wirelesscommunication terminal may transmit data different from the previouslytransmitted data to the wireless communication terminal that receivesthe data. Accordingly, the wireless communication terminal thattransmits the data may determine whether or not the wirelesscommunication terminal that receives the data receives the data. In aspecific embodiment, if the ACK policy indicates that the wirelesscommunication terminal that receives the data is to transmit ACKinformation immediately after data reception, the value of the fieldindicating the ACK policy may be 00.

In the embodiment of FIG. 17(a), while transmitting data to the firststation STA1 and the second station STA2, the access point AP sets theACK policy to transmit the ACK information immediately after thewireless communication terminal receiving the data receives data. Atthis time, the access point AP transmits a DL MU PPDU including thetrigger MPDU and the data MPDU to the first station STA1 and the secondstation STA2.

The first station STA1 and the second station STA2 receive the data andimmediately transmit the BA MPDU for the received data to the accesspoint AP. At this time, the first station STA1 and the second stationSTA2 transmit the UL MU PPDU including the BA MPDU and the data MPDUtogether. At this time, the ACK policy indicates that the wirelesscommunication terminal that receives the data transmits the ACKinformation immediately after the data reception.

The access point AP receives data from the first station STA1 and thesecond station STA2. The access point AP immediately transmits the BAMPDU for the received data to the first station STA1 and the secondstation STA2. At this time, the access point AP transmits the DL MU PPDUincluding the BA MPDU and the data MPDU together.

In addition, the ACK policy may indicate that the wireless communicationterminal receiving the data does not need to transmit the ACKinformation. At this time, the wireless communication terminal receivingthe data receives the data and does not transmit the ACK information. Ina specific embodiment, if the ACK policy indicates that the wirelesscommunication terminal receiving the data does not need to transmit theACK information, the value of the field representing the ACK policy maybe binary 10.

In addition, the ACK policy may indicate that the wireless communicationterminal receiving the data does not transmit the ACK or transmits theACK in the PSMP section. In a specific embodiment, if the ACK policyindicates that the wireless communication terminal receiving the datadoes not transmit the ACK or transmit the ACK in the PSMP section, thevalue of the field indicating the ACK policy may be binary 01.

In addition, the ACK policy may indicate that the wireless communicationterminal receiving the data transmits BA information when receiving aseparate BAR frame. At this time, the wireless communication terminalreceiving the data may store the reception status for each MPDU, and maytransmit the BA information when receiving the BAR frame. The wirelesscommunication terminal may transmit a PPDU including a BAR MPDU and atrigger MPDU together. At this time, the wireless communication terminalmay transmit the BAR MPDU before transmitting the trigger MPDU.Specifically, the wireless communication terminal may transmit thetrigger MPDU to the last MPDU included in the PPDU. The BAR MPDU is aresponse request at the MAC layer, and the trigger MPDU is an MPDUrequesting a response at the physical layer. Therefore, in order tostart data generation preparation first at the MAC layer, the wirelesscommunication terminal receiving the data may transmit the BAR MPDUbefore the trigger MPDU. Also, the wireless communication terminal maytransmit the BA MPDU before data MPDU transmission. As described above,the wireless communication terminal may transmit the BA MPDU to thefirst MPDU included in the PPDU.

In a specific embodiment, when the ACK policy indicates that thewireless communication terminal receiving the data transmits the BAinformation in the case of receiving a separate BAR frame, the value ofthe field indicating the ACK policy may be binary 11.

In the embodiment of FIG. 17(b), the access point AP sets the ACK policyto transmit the BA information when the wireless communication terminalreceiving the data receives the separate BAR frame while transmittingdata to the second station STA2. In addition, while transmitting data tothe first station STA1 and the third station STA3, the access point APsets the ACK policy to transmit the ACK information immediately afterthe wireless communication terminal receiving the data receives data. Atthis time, the access point AP transmits a DL MU PPDU including thetrigger MPDU and the data MPDU to the first station STA1 and the thirdstation STA3.

The first station STA1 and the third station STA3 receive the data andimmediately transmit the BA MPDU for the received data to the accesspoint AP. At this time, the first station STA1 and the third stationSTA3 transmit the UL MU PPDU including the BA MPDU and the data MPDUtogether. At this time, the ACK policy indicates that the wirelesscommunication terminal that receives the data transmits the ACKinformation immediately after the data reception.

The access point AP receives data from the first station STA1 and thethird station STA3. The access point AP immediately transmits the BA forthe received data to the first station STA1 and the third station STA3.At this time, the access point AP transmits the DL MU PPDU including theBA MPDU and the data MPDU together. In addition, the access point AP maytransmit the BAR MPDU and the trigger MPDU while transmitting data tothe second station SAT2. At this time, the BAR MPDU includes a StartingSequence Number (SSN). Specifically, the SSN instructs to transmitwhether or not to receive the MPDU corresponding to the sequence numberafter the sequence number indicated by the SSN. The access point APfirst transmits the BAR MPDU to the second station SAT2 rather than thetrigger MPDU.

The first to third stations STA1 to STA3 transmit the BA MPDU to theaccess point AP. At this time, the second station STA2 transmits a BAMPDU indicating whether to receive the MPDU corresponding to thesequence number after the sequence number indicated by the SSN.

Unlike the above-described embodiments, the first wireless communicationterminal may transmit the trigger MPDU to start the cascadingtransmission. At this time, the first wireless communication terminalmay set the TXOP of the cascading sequence based on the traffic priorityof the UL MU PPDU to be transmitted first. In the embodiment of FIG.17(c), the access point AP transmits a broadcast trigger MPDU to thefirst station STA1 and the second station STA2. The access point AP setsthe TXOP of the cascading sequence based on the traffic priority of theUL MU PPDU to be transmitted from the first station STA1 and the secondstation STA2.

The first station STA1 and the second station STA2 transmit data to theaccess point AP based on the broadcast trigger MPDU. At this time, theACK policy indicates that the wireless communication terminal thatreceives the data transmits the ACK information immediately after thedata reception.

The access point AP receives data from the first station STA1 and thesecond station STA2. The access point AP immediately transmits an ACKMPDU to the first station STA1 and the second station STA2. At thistime, the access point AP transmits the PPDU including the BA MPDU, thedata MPDU, and the trigger MPDU.

FIG. 18 illustrates a method for a wireless communication terminal torecover a cascading sequence when ACK information is not received in thecascading sequence according to an embodiment of the present invention.

The wireless communication terminal that does not receive the ACKinformation in the cascading sequence may transmit the PPDU includingthe data again. In the embodiment of FIG. 18(a), the access point APtransmits a PPDU including a plurality of data MPDUs data 1, data 2, anddata 3 and a trigger MPDU to the first station SAT1. At this time, thefirst station STA1 fails to receive the trigger MPDU. Therefore, thefirst station STA1 may not use the uplink transmission opportunityallocated to the first station STA1. Accordingly, the access point APagain transmits a plurality of data MPDUs data 1, data 2, and data 3 anda PPDU including a trigger MPDU. When the PPDU including the data isretransmitted as described above, it may occur that the first stationSTA1 transmits the normally received data again as in the embodiment ofFIG. 18(a).

In another specific embodiment, a wireless communication terminal thatfails to receive ACK information in a cascading sequence may transmit aBAR frame after a cascading sequence. In the embodiment of FIG. 18(b),the access point AP transmits a PPDU including a plurality of data MPDUsdata 1, data 2, and data 3 and a trigger MPDU to the first station SAT1.At this time, the first station STA1 fails to receive the trigger MPDU.Therefore, the first station STA1 may not use the transmissionopportunity allocated to the first station STA1. Accordingly, after thecascading sequence ends, the access point AP transmits a BAR frame tothe first station STA1. Through this, the access point AP receives theBA frame and determines whether or not the first station STA1 receivesthe plurality of data MPDUs data 1, data 2, and data 3 through the BAinformation. Also, the access point AP sets the SSN of the BAR frame to1, which is the start sequence number of the data MPDU that does notreceive the BA MPDU. When the first wireless communication terminaltransmits a BAR MPDU after a cascading sequence, a separate SU PPDU typeBAR frame and BA frame transmission is required. Therefore, when thefirst wireless communication terminal transmits the BAR frame after thecascading sequence, resource waste may occur compared to a case wherethe first wireless communication terminal transmits the BAR MPDU throughthe MU PPDU.

In another specific embodiment, a wireless communication terminal thatfails to receive ACK information in a cascading sequence may transmit aBAR MPDU in a cascading sequence. In the embodiment of FIG. 18(c), theaccess point AP transmits a PPDU including a plurality of data MPDUsdata 1, data 2, and data 3 and a trigger MPDU to the first station SAT1.At this time, the first station STA1 fails to receive the trigger MPDU.Therefore, the first station STA1 may not use the uplink transmissionopportunity allocated to the first station STA1. At this time, theaccess point AP transmits the BAR MPDU to the first station STA1 in thecorresponding cascading sequence. At this time, the access point AP maytransmit the PPDU including the BAR MPDU and the data MPDU together asin the embodiment of FIG. 18(c). Through this, waste of transmissionresources may be prevented. Further, the access point AP sets the SSN ofthe BAR MPDU to 1, which is the start sequence number of the data MPDUthat does not receive the BA MPDU.

In the embodiment of FIG. 18(d), the access point AP fails to receivethe BA MPDU transmitted from the first station STA1. The access point APtransmits the BAR MPDU to the first station STA1 in the cascadingsequence as described with reference to FIG. 18(c).

In the case where the BA is not received from the counterpart wirelesscommunication terminal, not only the first wireless communicationterminal but also the second wireless communication terminal maytransmit the BAR MPDU in the cascading sequence. In the embodiment ofFIG. 18(e), the first station STA1 transmits a PPDU including aplurality of data MPDUs data 1, data 2, and data 3 to the access pointAP. The access point AP transmits a BA MPDU for a plurality of dataMPDUs data 1, data 2, and data 3 to the first station STA1. At thistime, the first station STA1 fails to receive the BA MPDU for theplurality of data MPDUs data 1, data 2, and data 3. Accordingly, thefirst station STA1 transmits the BAR MPDU to the AP in the correspondingcascading sequence. At this time, the first station STA1 may transmitthe PPDU including the BAR MPDU and the data MPDU together as in theembodiment of FIG. 18(e). In addition, the first station STA1 may setthe SSN of the BAR MPDU to 1. If there is no data to be transmitted fromthe access point AP to the first station STA1, the access point AP maydelay transmission of the BA MPDU to the first station STA1. In thiscase, the access point AP may, in principle, transmit the BA MPDU withinthe corresponding TXOP.

In the case of restoring the cascading sequence through the embodimentsdescribed with reference to FIGS. 18(c) to 18(e), the wirelesscommunication terminal must transmit a separate BAR MPDU. Therefore,radio resources for transmitting the BAR MPDU are consumed. The wirelesscommunication terminal may request transmission of the ACK informationfor the MPDU previously transmitted through the MAC header of the dataMPDU. In this case, the wireless communication terminal may not consumeradio resources to transmit the BAR MPDU. This will be described withreference to FIG. 19.

FIG. 19 shows that a wireless communication terminal according to anembodiment of the present invention requests transmission of ACKinformation for an MPDU previously transmitted through a MAC header of adata MPDU.

The wireless communication terminal may request transmission of the ACKinformation for the MPDU previously transmitted through the MAC headerof the data MPDU. Specifically, the wireless communication terminal setsthe ACK policy of the data MPDU to transmit ACK information immediatelyafter data reception, so that the wireless communication terminal mayrequest to transmit a BA MPDU indicating whether it receives apreviously received MPDU in the corresponding cascading sequence.

In the embodiment of FIG. 19(a), the access point AP transmits a PPDUincluding a plurality of data MPDUs data 1, data 2, and data 3 and atrigger MPDU to the first station SAT1. At this time, the first stationSTA1 fails to receive the trigger MPDU. Therefore, the first stationSTA1 may not use the uplink transmission opportunity allocated to thefirst station STA1. Then, the access point AP requests transmission ofthe BA frame for the previously transmitted data MPDU data 1, data 2,and data 3 through the ACK policy of the data MPDU data 4, data 5, anddata 6 transmitted to the first station STA1 in the cascading sequence.At this time, the ACK policy may indicate to transmit ACK informationimmediately after data reception. In a specific embodiment, the value ofthe field representing the ACK policy may be 0. The first station STA1transmits to the access point AP a BA MPDU for a plurality of data MPDUsdata 1, data 2, data 3, data 4, data 5, and data 6 including the dataMPDU set with the ACK policy and the data MPDU received before the dataMPDU set with the ACK policy.

In the embodiment of FIG. 19(b), the access point AP fails to receivethe BA MPDU transmitted from the first station STA1. Accordingly, theaccess point AP requests transmission of the BA information on theprevious data MPDU data 1, data 2, and data 3 through the ACK policy ofthe data MPDUs data 4, data 5, and data 6 transmitted to the firststation STA1 in the cascading sequence.

When the first wireless communication terminal don't receive the BAMPDU, the first wireless communication terminal as well as the secondwireless communication terminal may request the BA informationtransmission by setting the ACK policy of the data frame in thecascading sequence. In the embodiment of FIG. 19(c), the first stationSTA1 transmits a PPDU including a plurality of data MPDUs data 1, data2, and data 3 to the access point AP. The access point AP transmits a BAMPDU for a plurality of data MPDUs data 1, data 2, and data 3 to thefirst station STA1. At this time, the first station STA1 fails toreceive the BA MPDU for the plurality of data MPDUs data 1, data 2, anddata 3. Accordingly, the first station STA1 requests transmission of theBA information on the previously transmitted data MPDUs data 1, data 2,and data 3 through the ACK policy of the data MPDUs data 4, data 5, anddata 6 transmitted to the first station STA1 in the cascading sequence.At this time, the ACK policy may indicate to transmit ACK informationimmediately after data reception. In a specific embodiment, the value ofthe field representing the ACK policy may be 0. The access point APtransmits to the first station STA1 a BA MPDU for a plurality of dataMPDUs data 1, data 2, data 3, data 4, data 5, and data 6 including thedata MPDU set with the ACK policy and the data MPDU received before thedata MPDU set with the ACK policy. If there is no data to be transmittedfrom the access point AP to the first station STA1, the access point APmay delay transmission of the BA MPDU to the first station STA1. In thiscase, the access point AP may, in principle, transmit the BA MPDU withinthe corresponding TXOP.

FIG. 20 shows a method of setting an ACK policy by a wirelesscommunication terminal according to an embodiment of the presentinvention.

The first wireless communication terminal may not set the ACK policy ofthe data transmitted from the plurality of second wireless communicationterminals. At this time, each of the plurality of second wirelesscommunication terminals may arbitrarily set an ACK policy of data to betransmitted to the first wireless communication terminal. The durationof a multi-station BA (M-STA BA or M-BA) frame indicating whether datais received may be limited to a certain length or less. If the durationof the M-BA frame becomes large, it may cause collision with legacyhidden nodes. However, in such an environment, if the first wirelesscommunication terminal does not set the ACK policy of the datatransmitted from the plurality of second wireless communicationterminals, the same problem as the embodiment of FIG. 20(a) may arise.

In the embodiment of FIG. 20(a), the access point AP transmits thetrigger MPDU to the first station STA1 to the fifth station STA5.

The first to fifth stations STA1 to STA5 transmit data to the accesspoint AP based on the trigger frame. At this time, the first to fourthstations STA1 to STA4 set the ACK policy of the data to be transmittedto immediately transmit the ACK information. The fifth station STA5 setsthe ACK policy of the data to be transmitted to transmit the BAinformation when receiving a separate BAR frame.

The access point AP transmits, due to the size limitation of the M-BAframe, an M-BA frame indicating only whether the data transmitted fromthe first station STA1 to the third station STA3 is received and notindicating whether the data transmitted from the fourth station STA4 tothe first station STA1 to the third station STA3 is received.

The fifth station STA5 transmits the BAR frame to the access point AP.At this time, the fourth station STA4 determines that the access pointAP does not receive the data, and transmits the data again to the accesspoint AP. Therefore, the fourth station STA4 repeatedly transmits datato the access point AP. Various embodiments for solving this problemwill be described with reference to FIGS. 20(b) to 20(d).

The first wireless communication terminal may set the ACK policy of thedata transmitted from the plurality of second wireless communicationterminals through the trigger information. Specifically, the firstwireless communication terminal may set the ACK policy of the datatransmitted from the plurality of second wireless communicationterminals through the trigger frame transmitted to the plurality ofsecond wireless communication terminals. At this time, the secondwireless communication terminal may set the ACK policy of the data to betransmitted based on the trigger frame.

For example, in the embodiment of FIG. 20(b), the access point APtransmits a trigger frame to the first station STA1 to the fifth stationSTA5. At this time, the access point AP sets the ACK policy of the datatransmitted from the first station STA1 to the third station STA4 toimmediately transmit the ACK information. In addition, the access pointAP sets the ACK policy of data transmitted from the fourth station tothe fifth station STA4 to STA5 to transmit a BA frame when receiving aseparate BAR frame.

The first to fifth stations STA1 to STA5 transmit data to the accesspoint AP based on the trigger frame. At this time, the first to thirdstations STA1 to STA3 set the ACK policy of the data to be transmittedto immediately transmit the ACK information. The fourth to fifthstations STA4 to STA5 set the ACK policy of the data to be transmittedto transmit the BA MPDU when receiving a separate BAR frame.

The access point AP transmits an M-BA MPDU indicating whether the datatransmitted from the first station to the third station STA1 to STA3 isreceived to the first station to the third station STA1 to STA3.

The fourth station STA4 transmits the BAR frame to the access point AP.The access point AP transmits a BA frame to the fourth station STA4.

The fifth station STA5 transmits the BAR frame to the access point AP.The access point AP transmits a BA frame to the fifth station STA5.

In another specific embodiment, the first wireless communicationterminal may signal whether to transmit additional ACK information whenACK information is transmitted. Accordingly, the first wirelesscommunication terminal may solve the problem described in 20(a) withoutsetting the ACK policy of the data transmitted from the plurality ofsecond wireless communication terminals. When the first wirelesscommunication terminal signals that there will be additional ACKinformation transmission at the time of transmitting the ACKinformation, the plurality of second wireless communication terminalsmay wait for a predetermined time without transmitting the data to thefirst wireless communication terminal again. If the BA frame is notreceived within a predetermined time, the second wireless communicationterminal may transmit data again.

For example, in the embodiment of FIG. 20(c), the access point APtransmits a trigger frame to the first station STA1 to the fifth stationSTA5.

The first to fifth stations STA1 to STA5 transmit data to the accesspoint AP based on the trigger frame. At this time, the first to fifthstations STA1 to STA5 set the ACK policy of the data to be transmittedto immediately transmit the ACK information.

The access point AP transmits, due to the size limitation of the M-BAframe, an M-BA frame indicating whether the data transmitted from thefirst station STA1 to the third station STA3 is received and notindicating the data transmitted from the fourth station STA4 to thefifth station STA5 to the first station STA1 to the third station STA3is received. At this time, the access point AP transmits informationindicating that the ACK MPDU is to be further transmitted, through theM-BA frame.

Since the access point AP transmits information indicating that theaccess point AP will further transmit an ACK MPDU, the fourth stationSTA4 to the fifth station STA5 do not transmit data again.

The access point AP transmits an M-BA frame indicating whether the datatransmitted from the fourth station STA4 to the fifth station STA5 isreceived or not to the fourth station STA4 to the fifth station STA5.

In another specific embodiment, the first wireless communicationterminal may signal whether the additional BA frame is transmittedthrough the duration size of the PPDU including the ACK information whenthe ACK information is transmitted. Specifically, when the ACKinformation is transmitted, the first wireless communication terminalsets a duration size of a PPDU including ACK information to a valuelarger than a predetermined size, thereby signaling that an additionalBA frame is to be transmitted. At this time, the predetermined time maybe designated by a PPDU duration required when ACK information istransmitted through a basic MCS or a value obtained by addingDistributed Inter Frame Space (DIFS) to a PPDU duration required whenACK information is transmitted through a basic MCS.

For example, in the embodiment of FIG. 20(d), the access point APtransmits a trigger frame to the first station to the fifth station STA1to STA5.

The first to fifth stations STA1 to STA5 transmit data to the accesspoint AP based on the trigger frame. At this time, the first to fifthstations STA1 to STA5 set the ACK policy of the data to be transmittedto immediately transmit the ACK information.

At this time, the access point AP receives the data transmitted from thefirst station to the fourth station STA1 to STA4 and fails to receivethe data transmitted from the fifth station STA5.

The access point AP transmits an M-BA frame indicating whether the datatransmitted from the first station to the third station STA1 to STA3 isreceived to the first station to the third station STA1 to STA3. At thistime, the access point AP sets the duration size of the PPDU includingthe M-BA frame to a value larger than a predetermined size (Max ACKDuration), and signals the transmission of the additional ACKinformation.

Since the access point AP signals information indicating that the accesspoint AP will further transmit an ACK MPDU, the fourth station to thefifth station STA4 to STA5 do not transmit data again.

The AP transmits, to the fourth station STA4, a BA frame indicatingwhether the data transmitted from the fourth station STA4 is received ornot. At this time, the access point AP sets the duration size of thePPDU including the BA frame to a value smaller than a predetermined size(Max ACK Duration), and signals that there is no transmission of theadditional ACK information.

The fifth station STA5 transmits data again to the access point AP.

The access point AP transmits a BA frame to the fifth station STA5.

There may be a method of setting a network allocation vector (NAV) as amethod for increasing the transmission probability of controlinformation. This will be described with reference to FIG. 21.

FIG. 21 shows a method of a wireless communication terminal to set anetwork allocation vector (NAV) for communication with a plurality ofwireless communication terminals according to an embodiment of thepresent invention.

The wireless communication terminal may set the NAV to prevent anotherwireless communication terminal from connecting to the wireless mediumused for communication. The NAV allows a wireless communication terminalto reserve a specific wireless medium to be used. The NAV is set througha Multi User-Request To Send (MU-RTS) frame and a simultaneous Clear ToSend (CTS) frame in the communication between the first wirelesscommunication terminal and the plurality of second wirelesscommunication terminals. Specifically, the first wireless communicationterminal transmits an MU-RTS frame to a plurality of second wirelesscommunication terminals that are to transmit data. The plurality ofsecond wireless communication terminals simultaneously transmit thesimultaneous CTS frames having the same format to the first wirelesscommunication terminal. In such a case, the plurality of second wirelesscommunication terminals set all the same size NAVs to the surroundingwireless communication terminals. For example, in the embodiment of FIG.21(a), the access point AP transmits an MU-RTS frame to the firststation STA1 to the sixth station STA6.

The first to sixth stations STA1 to STA6 transmit a simultaneous CTSframe to the access point AP. Through such MU-RTS frame and simultaneousCTS frame transmission, the access point AP and the first station STA1to the sixth station STA6 set the NAV of the neighboring station. Atthis time, the first station STA1 to the sixth station STA4 all set theNAV of the same value. However, the first to fourth stations STA1 toSTA4 receive data faster than the fifth to sixth stations STA5 to STA6.Thus, it may be inefficient for all stations to set a NAV of the samesize.

Accordingly, the second wireless communication terminal may transmit theCTS frame at a necessary point within the cascading sequence.Accordingly, the plurality of second wireless communication terminalsmay set different NAVs to neighboring stations. Specifically, the firstwireless communication terminal transmits an MU-RTS frame to a secondwireless communication terminal that will first transmit data in thecascading sequence. Then, the first wireless communication terminaltransmits the trigger frame before transmitting the data to the secondwireless communication terminal that does not transmit the MU-RTS frame.The second wireless communication terminal receiving the trigger frametransmits the CTS frame based on the trigger frame. For example, in theembodiment of FIG. 21(b), the access point AP transmits an MU-RTS frameto the first station STA1 to the fourth station STA4.

The first to fourth stations STA1 to STA4 transmit a simultaneous CTSframe to the access point AP.

The access point AP transmits data to the first station to the fourthstation STA1 to STA4.

Then, the access point AP transmits the trigger frame to the fifthstation to the sixth station STA5 to STA6.

The fifth to sixth stations STA5 to STA6 transmit a simultaneous CTSframe to the access point AP.

At this time, the NAV of the CTS frame transmitted from the firststation STA1 to the fourth station STA4 may be the same as the NAV ofthe CTS frame transmitted from the fifth station to the sixth stationSTA5 to STA6. In another specific embodiment, the NAV of the CTS frametransmitted from the first station to the fourth station STA1 to STA4may be the time point until the data exchange ends between the firststation to the fourth station STA1 to STA4 and the access point AP.Through this operation, the first to sixth stations STA1 to STA6 may setthe NAV for each station.

In another specific embodiment, the second wireless communicationterminal may set a NAV by transmitting a simultaneous CTS frame withoutbeing based on an MU-RTS frame at a necessary point within a cascadingsequence. At this time, the second wireless communication terminal maytransmit the simultaneous CTS frame based on the triggering information.Accordingly, the second wireless communication terminal may reduce theoverhead due to the MU-RTS frame transmission. For example, in theembodiment of FIG. 21(c), the access point AP transmits the MU PPDUincluding trigger information to the first station STA1 to the fourthstation STA4.

The first to fourth stations STA1 to STA4 transmit the simultaneous CTSframe to the access point AP based on the trigger information.

Then, the access point AP transmits the trigger frame to the fifthstation to the sixth station STA5 to STA6.

The fifth to sixth stations STA5 to STA6 transmit the simultaneous CTSframe to the access point AP based on the trigger frame. Through thisoperation, the first to sixth stations STA1 to STA6 may set the NAVwithout receiving the MU-RTS frame.

In another specific embodiment, the first wireless communicationterminal may cancel the NAV by transmitting a CF-End frame.Specifically, when there is no simultaneous CTS frame transmission for apredetermined time from when the first wireless communication terminaltransmits the MU-RTS frame, the first wireless communication terminalmay transmit the CF-End frame. For example, in the embodiment of FIG.21(d), the access point AP transmits an MU-RTS frame to the firststation to the sixth station STA1 to STA6. The access point AP does notreceive the CTS frame from the first station to the sixth station STA1to STA6. Then, the access point AP cancels the set NAV by transmittingthe CF-End frame. Through this operation, the access point AP mayprevent the surrounding wireless communication terminals fromunnecessarily connecting to the wireless medium due to the preset NAVeven when communication with the station is impossible.

The trigger information described above may be used for random access ofa plurality of second wireless communication terminals. At this time,there is a need for a random access method that distributes theconnection time points of the plurality of second wireless communicationterminals and minimize the connection conflict between the secondwireless communication terminals. This will be described with referenceto FIG. 22.

FIG. 22 shows that a wireless communication terminal according to anembodiment of the present invention performs random access based on atrigger frame.

The RU allocation information included in the trigger frame may indicatean RU that is randomly accessible by a plurality of second wirelesscommunication terminals. The plurality of second wireless communicationterminals may be randomly accessed based on the trigger frame as in theembodiment of FIG. 22(a).

Specifically, the second wireless communication terminal may randomlyobtain a counter value within a predetermined range, and determinewhether to peform a random access based on the counter value. Inaddition, the second wireless communication terminal may determinewhether to perform a random access based on the number of RUs allocatedto the random access. This is because each of the plurality of secondwireless communication terminals may access each RU.

Specifically, the second wireless communication terminal randomlyobtains the counter value within a certain range, and when the countervalue is smaller than the number of RUs allocated to the random access,the second wireless communication terminal may randomly access the RUallocated to the random access. If the counter value is not smaller thanthe number of RUs assigned to the random access, the second wirelesscommunication terminal sets the counter value to a value obtained bysubtracting the number of RUs allocated to the random access from thecounter value. If the obtained counter value is smaller than the numberof RUs assigned to the random access, the second wireless communicationterminal may randomly access the RUs assigned to the random access. Ifthe counter value is not smaller than the number of RUs assigned to therandom access, the second wireless communication terminal repeats thesame process when receiving the next trigger MPDUMPDU. At this time, thesecond wireless communication terminal maintains the counter value untilthe next trigger frame is transmitted.

If the random access is determined, the second wireless communicationterminal may randomly select any one of the plurality of RUs assigned tothe random access.

In yet another specific embodiment, the second wireless communicationterminal may determine a random access by computing a random value foreach RU assigned to the random access. At this time, the second wirelesscommunication terminal may randomly access the RU whose random access isdetermined first. In yet another embodiment, the second wirelesscommunication terminal may randomly access all RUs whose random accessis determined first.

Also, the second wireless communication terminal may perform randomaccess with higher probability as the backoff-window counter value issmaller. Specifically, the predetermined range for obtaining theabove-described counter value may be the range of the backoff-windowcounter value. Also, in the case of determining random access bycalculating a random value for each RU, the second wirelesscommunication terminal may be determined to randomly access the RU witha higher probability as the backoff-window counter value is smaller. Atthis time, the second wireless communication terminal may obtain thebackoff-window counter value as in the embodiment of FIG. 22(b).

FIG. 23 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

Through the above-described embodiments, the first wirelesscommunication terminal 2301 may transmit control information.Specifically, the first wireless communication terminal 2301 maytransmit trigger information and data for triggering transmission of thesecond wireless communication terminal 2303 to the plurality of secondwireless communication terminals 2303 (S2301). The trigger informationmay include information on a resource unit (RU) assigned to theplurality of second wireless communication terminals 2303 andinformation indicating the length of a PPDU transmittable from thesecond wireless communication terminal 2303. The RU indicates a unit ofa frequency band allocated to the second wireless communication terminalby the first wireless communication terminal.

Specifically, the first wireless communication terminal 2301 maytransmit the trigger information to the plurality of second wirelesscommunication terminals 2303 through the MAC header included in theMPDU. At this time, the MPDU may be a data MPDU including data.

In another specific embodiment, the first wireless communicationterminal 2301 may transmit the A-MPDU including the data MPDU with thedata and the trigger MPDUMPDU to the plurality of second wirelesscommunication terminals 2303. At this time, the trigger MPDU may be thefirst MPDU among a plurality of MPDUs included in the A-MPDU. Asdescribed above, when the A-MPDU includes both the trigger MPDU and theBA MPDU, the BA MPDU may be the first MPDU among the plurality of MPDUsincluded in the A-MPDU. In addition, the A-MPDU may include a pluralityof trigger MPDUs including the same trigger information.

In a specific embodiment, the first wireless communication terminal 2301may transmit trigger information to the plurality of second wirelesscommunication terminals 2303 as in the embodiment described withreference to FIG. 8 to FIG. 16.

The second wireless communication terminal 2303 receives the triggerinformation from the first wireless communication terminal 2301, andtransmits the ACK information for the data based on the triggerinformation (S2303). Specifically, the second wireless communicationterminal 2303 may acquire the trigger information from the MAC header ofthe MPDU transmitted from the first wireless communication terminal2301. At this time, the second wireless communication terminal 2303 mayacquire the information on the RU assigned to the second wirelesscommunication terminal 2303 from the trigger information, and based onthe information on the RU allocated to the second wireless communicationterminal 2303, may transmit the ACK information. The second wirelesscommunication terminal 2303 may acquire length information indicatingthe length of a PLCP Protocol Data Unit (PPDU) including ACK informationfrom the trigger information, and may transmit ACK information based onthe length information. The second wireless communication terminal 2303may transmit ACK information and data based on the length information.In a specific embodiment, the second wireless communication terminal2303 may transmit data based on the remaining length excluding thelength required to transmit the ACK information from the lengthindicated by the length information. Also, the second wirelesscommunication terminal may transmit the management MPDU together withthe ACK information instead of the data. At this time, the ACKinformation may be ACK MPDU or BA MPDU.

When the second wireless communication terminal 2303 transmits ACKinformation and data together, the first wireless communication terminal2301 may transmit ACK information to the plurality of second wirelesscommunication terminals 2301. At this time, the first wirelesscommunication terminal 2301 may transmit ACK information as in theembodiment described with reference to FIG. 20.

The trigger information as described above may represent a frequencyband allocated for random access. Specifically, the trigger informationmay include information indicating one or more RUs assigned to a randomaccess. The second wireless communication terminal 2303 may randomlyobtain a counter value within a certain range and determine whether toperform a random access based on the counter value and the number of oneor a plurality of RUs allocated to the random access. When the randomaccess is determined, the second wireless communication terminal 2303may randomly access any one of the one or more RUs assigned to therandom access. Specifically, the second wireless communication terminal2303 may perform random access based on the trigger informationaccording to the embodiment described with reference to FIG. 22.

In addition, the first wireless communication terminal 2301 and thesecond wireless communication terminal 2303 may perform the recoveryprocedure according to the embodiments described with reference to FIGS.17 to 19 in the cascading sequence.

Further, the first wireless communication terminal 2301 and the secondwireless communication terminal 2303 may set the NAV as in theembodiment described with reference to FIG. 21 when data is transmittedbased on the trigger information.

Although the present invention is described by using wireless LANcommunication as an example, it is not limited thereto and may beapplied to other communication systems such as cellular communication.Additionally, while the method, device, and system of the presentinvention are described in relation to specific embodiments thereof,some or all of the components or operations of the present invention maybe implemented using a computer system having a general purpose hardwarearchitecture.

The features, structures, and effects described in the above embodimentsare included in at least one embodiment of the present invention and arenot necessary limited to one embodiment. Furthermore, features,structures, and effects shown in each embodiment may be combined ormodified in other embodiments by those skilled in the art. Therefore, itshould be interpreted that contents relating to such combination andmodification are included in the range of the present invention.

While the present invention is described mainly based on the aboveembodiments but is not limited thereto, it will be understood by thoseskilled in the art that various changes and modifications are madewithout departing from the spirit and scope of the present invention.For example, each component specifically shown in the embodiments may bemodified and implemented. It should be interpreted that differencesrelating to such modifications and application are included in the scopeof the present invention defined in the appended claims.

1. A wireless communication terminal that wirelessly communicates with abase wireless communication terminal, the wireless communicationterminal comprising: a transceiver; and a processor, wherein theprocessor configured to receive trigger information and data from thebase wireless communication terminal by using the transceiver, andtransmit ACK information indicating whether the data is received to thebase wireless communication terminal based on the trigger information,wherein the trigger information is information for triggeringtransmission of the wireless communication terminal.
 2. The wirelesscommunication terminal of claim 1, wherein the processor is configuredto obtain the trigger information from an MAC header of a MAC ProtocolData Unit (MPDU) transmitted from the base wireless communicationterminal.
 3. The wireless communication terminal of claim 2, wherein theprocessor is configured to obtain information on a Resource Unit (RU)allocated to the wireless communication terminal from the triggerinformation, and transmit the ACK information based on the informationon the RU allocated to the wireless communication terminal.
 4. Thewireless communication terminal of claim 2, wherein the processor isconfigured to obtain length information indicating a length of a PLCPProtocol Data Unit (PPDU) including the ACK information from the triggerinformation, and transmit the ACK information based on the lengthinformation.
 5. The wireless communication terminal of claim 4, whereinthe processor is configured to transmit the ACK information and data tothe base wireless communication terminal based on the lengthinformation.
 6. The wireless communication terminal of claim 5, whereinthe processor is configured to transmit data to the base wirelesscommunication terminal based on a remaining length excluding a lengthrequired for transmission of the ACK information from a length indicatedby the length information.
 7. The wireless communication terminal ofclaim 1, wherein the processor is configured to receive anAggregate-MPDU (A-MPDU) including a plurality of MPDUs by using thetransceiver, wherein the A-MPDU comprises a trigger MPDU including thetrigger information and a data MPDU including the data, wherein thetrigger MPDU is a first MPDU among a plurality of MPDUs included in theA-MPDU.
 8. The wireless communication terminal of claim 7, wherein theA-MPDU further comprises a trigger MPDU including the triggerinformation in addition to the trigger MPDU.
 9. The wirelesscommunication terminal of claim 1, wherein the trigger informationcomprises information indicating one or more RUs allocated to a randomaccess, wherein the processor is configured to obtain a counter valuerandomly within a predetermined range, and determine whether to performa random access based on the counter value and the number of the one ormore RUs allocated to the random access.
 10. The wireless communicationterminal of claim 9, wherein when a random access is determined, theprocessor is configured to randomly access any one of the one or moreRUs allocated to the random access.
 11. A base wireless communicationterminal that wireles sly communicates with a plurality of wirelesscommunication terminals, the base wireless communication terminalcomprising: a transceiver; and a processor, wherein the processor isconfigured to transmit trigger information to the plurality of wirelesscommunication terminals by the transceiver, and receive ACK informationindicating whether the data is received from the plurality of wirelesscommunication terminals.
 12. The base wireless communication terminal ofclaim 11, wherein the processor is configured to insert the triggerinformation into a MAC header of a MAC Protocol Data Unit (MPDU). 13.The base wireless communication terminal of claim 12, wherein thetrigger information comprises information on a resource unit (RU)allocated to each of the plurality of wireless communication terminals.14. The base wireless communication terminal of claim 13, wherein thetrigger information comprises length information indicating a length ofa PLCP Protocol Data Unit (PPDU) including the ACK information.
 15. Thebase wireless communication terminal of claim 11, wherein the processoris configured to transmit an Aggregate-MPDU (A-MPDU) including aplurality of MPDUs by using the transceiver, wherein the A-MPDUcomprises a trigger MPDU including the trigger information and a dataMPDU including the data, wherein the trigger MPDU is a first MPDU amongthe plurality of MPDUs included in the A-MPDU.
 16. The base wirelesscommunication terminal of claim 15, wherein the A-MPDU further comprisesa trigger MPDU including the trigger information in addition to thetrigger MPDU.
 17. The base wireless communication terminal of claim 15,wherein the processor is configured to transmit the trigger MPDU and thedata MPDU using a different Modulation & Coding Scheme (MCS) by usingthe transceiver.
 18. A method of operating a wireless communicationterminal that wirelessly communicates with a base wireless communicationterminal, the method comprising: receiving trigger information and datafrom the base wireless communication terminal; and transmitting ACKinformation indicating whether the data is received to the base wirelesscommunication terminal based on the trigger information, wherein thetrigger information is information for triggering transmission of thewireless communication terminal.
 19. The method of claim 19, wherein thereceiving of the trigger information and the data comprises obtainingthe trigger information from a MAC header of a MAC Protocol Data Unit(MPDU) transmitted from the base wireless communication terminal. 20.The method of claim 19, wherein the obtaining of the trigger informationfrom the MAC header comprises obtaining information on a Resource Unit(RU) allocated to the wireless communication terminal from the triggerinformation, wherein the transmitting of the ACK information comprisestransmitting the ACK information based on the information on the RUallocated to the wireless communication terminal.